Smiling widely, the Queen stepped down from her plane to begin a trip 100 years in the making.
Suitably dressed in green, she became the first reigning monarch to set foot in the Irish Republic.
Click on photo for gallery Every footstep signalled a building of bridges – the beginning of a new era in British-Irish relations.
As Her Majesty greeted officials, she was joined by her husband the Duke of Edinburgh.
The royal couple were conveyed to the impressive official residence of President Mary McAleese in Phoenix Park, Dublin, where they were to be officially welcomed to the Republic.
In 1911 George V, the Queen's grandfather, visited Ireland when it was still part of the UK. Then Ireland gained independence and relations between the two countries became strained.
The monarch's exact itinerary is not known, but the visit will last four days and cover four Irish counties - Dublin, Kildare, Tipperary and Cork.
She will visit the Garden of Remembrance in the capital which commemorates the people who died fighting for Irish independence.
There'll be no apology for the bloodshed as some had hoped, but the Queen will lay a wreath in their memory.
Also on the agenda is Croke Park - the scene of Bloody Sunday - one of the darkest episodes in British-Irish history.
This was when British soldiers killed 14 spectators at a Gaelic football match in 1920 after the Irish Republican army had killed 14 British intelligence agents.
She will also be shown locations of significance to the royal family, including a tree planted by Queen Victoria 150 years ago.
There have been protests, but most people welcome the trip. Among those happy about it are X Factor contestant Mary Byrne, who will sing for the royal visitors during a special concert.
"I never dreamed I would see the Queen come to Ireland," she said. "We have moved on so far for this to be able to happen and I know the majority of people feel the same way.
Security is high on the trip. Around 8,000 gardai or national police officers, and 2,000 soldiers are involved.
There will be no spontaneous walkabouts or handshakes – crowds will be kept behind metal barriers at least 40ft from the Queen.
And the VIP royals will be driven to every event in bullet proof cars.
The alarm was raised on Tuesday morning when an improvised explosive device, thought to be a pipe bomb, was found on a crowded coach heading from the west of Ireland just 40 miles from Dublin.